Conventionally, refrigeration cycle apparatuses in which a chlorofluorocarbon or an alternative chlorofluorocarbon is used as a refrigerant are widely used. However, such refrigerants are responsible for the problems such as ozone depletion and global warming. In view of this, refrigeration cycle apparatuses have been proposed in which water is used as a refrigerant that places only an extremely small load on the global environment. As an example of such a refrigeration cycle apparatus, Patent Literature 1 discloses a refrigeration cycle apparatus 100 as shown in FIG. 5.
The refrigeration cycle apparatus 100 has a refrigerant circuit 110 composed of an evaporator 111, a compressor 112, and a condenser 113 which are connected in this order. Water is retained in the evaporator 111 and the condenser 113. The water retained in the evaporator 111 is circulated via a low temperature-side load unit 121 by a circulation path for heat absorption 120. The water retained in the condenser 113 is circulated via a high temperature-side load unit 131 by a circulation path for heat release 130. The circulation paths 120 and 130 are provided with pumps 122 and 132, respectively. The compressor 112 draws water vapor from the evaporator 111, compresses the water vapor, and discharges the compressed water vapor to the condenser 113.
In the case of using water as a refrigerant as in the refrigeration cycle apparatus 100 of Patent Literature 1, the difference between a high-pressure-side pressure Pc and a low-pressure-side pressure Pe is reduced due to the physical properties of water, compared to the case of a refrigeration cycle in which a chlorofluorocarbon or an alternative chlorofluorocarbon is used as a refrigerant. Accordingly, the use of water as a refrigerant has a problem in that a high-precision expansion valve and complicated control of the valve are needed. In order to address this problem, the refrigeration cycle apparatus 100 described in Patent Literature 1 eliminates the need for a high-precision expansion valve and complicated control of the valve by being configured to ensure a predetermined difference between the high-pressure-side pressure Pc and the low-pressure-side pressure Pe by means of a level difference Δh between a water level in the evaporator 111 and a water level in the condenser 113. This can make it easy to control a system using water as a refrigerant, resulting in improvement in the reliability of a refrigeration cycle apparatus.